Repeaters, distributed antenna systems, and similar systems are communications systems that are used to extend wireless coverage into areas where the radio signals from base stations (BTS) are often very attenuated or absent. Those areas might be inside buildings, in tunnels, located in shadowed areas that are behind mountains or in underground train systems, as well as other isolated areas. Generally, applications for such communications systems involve installations where the repeater or distributed antenna system is immobile and is mounted in a permanent location. That is, it is a fixed installation.
In other applications, the area that has limited penetration of the RF signals is mobile. That is, the repeater or distributed antenna system is installed in a moving or mobile system such as a train, a ship, a car, a bus or an airplane. This application presents unique performance issues not encountered in fixed installations.
When a repeater or distributed antenna systems (DAS system) is used in a mobile application, the environment in which it is operating is constantly changing. As the repeater or DAS system moves through different areas, the wanted and unwanted signals processed by the repeater or DAS system change in level as it nears and then moves away from the sources of those signals. Additionally, the signals processed by the repeater or DAS system can change in frequency as the system passes in and out of the range of different signal sources. Repeaters and DAS systems used in these environments are designed to accommodate these changes, but certain combinations of signals at specific locations may cause a system to function poorly.
Another unique characteristic of mobile applications of repeaters or DAS systems is the rate at which its operating environment can change. In fixed installations, the environment is usually quite static and any changes can be accommodated through slow adaptation of the repeater or DAS system. However, in mobile installations the signal environment can be very dynamic, and the conditions that require modified operation may exist for only a short period of time. Therefore, a repeater or DAS system used in a mobile installation must adapt very rapidly if it needs to accommodate those changes. Typically, a repeater or DAS system adapts its operation in a reactive manner. In other words, it modifies its operation after it detects the conditions that require a change in its operation. Operating in a reactive manner in slowly changing environments is acceptable, but in rapidly changing mobile environments operating in a reactive manner can lead to poor performance because the condition may have come and gone before the system is able to react to the change and to modify its operation.